The present invention relates to a method and a device for producing a pneumatic vehicle tire with a radial carcass, belt layers, and a tread from a green tire in a radially divided vulcanization mold having a plurality of radial segments wherein the ratio between a tread portion to be filled by a high interior pressure in the vulcanization mold and the tire tread depth is smaller than 1 so that before completely closing the vulcanization mold the radial segments come into contact with the green tire.
The present invention is based on the prior art represented by European patent 0 405 276 and German Offenlegungsschrift 40 09 500. These prior art documents deal with the problem that during closing of the radial segments of radially divided vulcanization molds the still flowable rubber is forced into the essentially axially extending gaps of the radial segments which form the tread of the vehicle tire resulting in thickened portions at the finished tire product and in a radial force increase when such thickened portions come into contact with the road surface during driving. This results in vibrations of the belt package relative to the bead cores and also, to some extent, in vibrations of the entire wheel suspension system. This problem is especially pronounced with tread profilings extending essentially in the circumferential direction of the tire.
In both prior art documents this problem is solved by providing an increased positive volume at the segment borders in order to accommodate the excess rubber material within the finished tire in a manner which is not detrimental to the trueness of the tire, whereby the aforementioned European patent suggests the extension of the additional volume on both sides of the respective segment border, while the German Offenlegungsschrift has recognized that this is not a necessary requirement and that the additional volume must only be arranged within the area of the segment borders.
Tires that are produced according to these prior art documents demonstrate an excellent behavior with respect to the radial force variations when measured in a quasi-statical method, however, the radial force variations become worse with increasing velocity. This negative effect is more pronounced at non-driven axles than at driven axles. The effect is greater with tires having a hard rubber mixture than with tires comprised of a soft rubber mixture. The problem is most pronounced at non-driven front axles of utility vehicles, especially trucks.
The increase of the radial force variations as a function of the velocity has not been recognized in the prior art, most likely because the body sound conducted through solids and the noise level Generally increase with the velocity and mask this behavior.
It is therefore an object of the present invention to lower the radial force variations especially at higher velocities.